As electrophotographic photosensitive members, general are cylindrical electrophotographic photosensitive members (hereinafter, also simply referred to as “electrophotographic photosensitive members”) each including a photosensitive layer formed on a cylindrical substrate. Among electrophotographic photosensitive members, organic electrophotographic photosensitive members including photosensitive layers (organic photosensitive layers) using organic materials as photoconductive materials (charge generating materials and charge transporting materials) have come into wide use. As organic electrophotographic photosensitive members, because of the advantages involving high sensitivity and versatility of material design, predominantly used are electrophotographic photosensitive members each having a laminated photosensitive layer formed by laminating a charge generating layer including a charge generating material and a charge transporting layer including a charge transporting material.
In the image forming process, electrophotographic photosensitive members are used in the repeated cycles of the processes of charging, exposing, developing, transferring and cleaning (and charge removing). In particular, the cleaning process for removing the residual toner staying on the surface of the electrophotographic photosensitive member after the transfer process is an important process for the purpose of obtaining clear images. As the cleaning method, common are the methods in each of which a rubber cleaning blade is pressed against the electrophotographic photosensitive member and thus the residual toner is scraped.
However, cleaning blades exhibiting excellent cleaning capability are large in frictional force with the surface of the electrophotographic photosensitive member, and hence tends to cause problems such as the driving torque increase, the slipping away of the toner due to the micro-vibration of the cleaning blade and the inversion of the cleaning blade. The effects of the size reduction and higher performances of toner particles according to a recent trend toward higher image quality on the cleaning performances are also dealt with.
Among the methods for solving the aforementioned problems, there is a method in which the surface of the electrophotographic photosensitive member is appropriately roughened. This method is effective in reducing the contact area between the surface of the electrophotographic photosensitive member and the cleaning blade and in reducing the frictional force.
Various methods are known for such surface roughening of the surface of the electrophotographic photosensitive member; however, in particular, for the purpose of effectively reducing the frictional force, it is necessary to finely control the surface shape and condition of the electrophotographic photosensitive member. As such a method, PTL 1 discloses a technique for compression molding processing by bringing a touch roll or a molding member (a mold) having an uneven structure on the surface thereof into contact with the surface of the electrophotographic photosensitive member. PTL 1 describes an example in which a SUS 304 touch roll having a prismatic and wavy structure is brought into contact with an electrophotographic photosensitive member by applying a force of 2×10−4 N, and thus, for example, a wavy structure having a pitch of 5 μm and an average depth of 5 μm is formed on the surface of the electrophotographic photosensitive member. PTL 1 also describes an example in which by using a molding member having a well-type structure in which wells having an average one side length of 100 nm and an average depth of 100 nm are formed with an inter-pitch distance of 100 nm, the surface of the electrophotographic photosensitive member was compressed for 2 minutes with a force of 0.8 N, and consequently, there has been formed, on the surface of the electrophotographic photosensitive member, a well-type structure in which wells having an average one side length of 70 nm and a depth of 30 nm are formed with an inter-pitch distance of 120 nm. It has also been disclosed that by heating the electrophotographic photosensitive member and the molding member during processing, the molding accuracy is improved, and the processing pressure is set at 1 N or less for the purpose of maintaining the circularity of the electrophotographic photosensitive member.
The compression molding processing technique disclosed in PTL 1 is an application of a heretofore known technique, to electrophotographic photosensitive members, such as an emboss processing technique, which is an uneven structure processing method for resin surface and others, or a nanoimprint technique which has recently been studied actively as a microprocessing technique.
In general, conventional techniques for performing uneven structure formation processing on the surface of resin films or resin moldings are performed according to the following steps as described in PTL 2:
(1) a resin to be processed is heated to a temperature equal to or higher than the glass transition temperature of the resin (a step of softening the resin so as to easily undergo thermal deformation);
(2) a molding member (a mold) is heated to a temperature equal to or higher than the glass transition temperature of the resin and brought into pressure contact with the resin (a step of penetrating the resin into the fine structures of the molding member);(3) after a predetermined elapsed time, the resin and the molding member are cooled down to a temperature equal to or lower than the glass transition temperature (a step of fixing the fine structure);(4) the molding member is released from the resin.
According to the above-described steps, a batch transfer of the fine structure is possible for the whole area of the surface (the surface having the surface structure (uneven structure) corresponding to the uneven structure formed on the surface of the cylindrical electrophotographic photosensitive member) of the molding member, and thus it is possible to process different workpieces separately (a batch method) according to the above-described steps. In sheet-like workpieces, while the workpieces are being moved, the transfer of the surface structure of the whole area of the surface (the surface having the uneven structure) of the molding member can be repeatedly performed (a step-and-repeat method). In the above-described steps, the heating steps and the cooling steps are important. When the heating temperature is low, there tends to occur a problem such that no sufficient surface structure transfer is able to be performed, and when the cooling is not sufficient, there tends to occur a problem such that the transferred surface structure is collapsed. Accordingly, the control conditions in the heating steps and the cooling step are preferably optimized in detail according to the different properties of the resin.
With respect to the temperature control of each of the members being processed, PTL 3 discloses the control methods focusing respectively on the molding member and the workpiece such as a resin film.
When the whole of the surface (the surface having an uneven structure) of the molding member is pressed against the workpiece, the uniformization of the abutting pressure within the area of the surface (the surface having an uneven structure) of the molding member is an important factor. The workpieces in the above-described conventional techniques are assumed to have flat plate shapes or to be flexible materials; however, in the cylindrical electrophotographic photosensitive member, which is the workpiece in the present invention, the surface to be processed has a curvature, and an object to be processed is a resin layer (a surface layer) having a thickness of a few microns to a few tens microns, formed on a cylindrical substrate being comparatively small in the elastic deformation magnitude and having a hardness. Accordingly, it is difficult to perform the contact between such a surface and the molding member, with a satisfactory precision.
For the purpose of overcoming this difficulty, various inventions and improvements have hitherto been made. Among such inventions and improvements, there is a method in which as shown in FIG. 3, a plate-like molding member 5 is bonded onto a flat-plate-like supporting member 13, and a columnar insert 12 is inserted into the interior of (made to pass through) a cylindrical electrophotographic photosensitive member 1, which is a workpiece. In this method, as described in PTL 3, by applying force (pressure), with some sort of unit, toward the molding member, on both end portions of the insert in the axial direction thereof, the surface layer 3 of a cylindrical substrate 2 of the cylindrical electrophotographic photosensitive member 1 is pressurized while being pressed against the molding member 5, across the width of the surface layer 3 along the axial direction of the cylindrical electrophotographic photosensitive member 1.
In this method, the outer diameter of the insert to be inserted into the cylindrical electrophotographic photosensitive member is required to be smaller than the inner diameter of the cylindrical substrate of the cylindrical electrophotographic photosensitive member as the workpiece. The length of the part of the insert, abutting on the cylindrical substrate, is required to be a length approximately corresponding to the length in the axial direction of the cylindrical substrate of the cylindrical electrophotographic photosensitive member. The shape of the insert satisfying such conditions is often long and thin. For example, the inner diameter of the cylindrical substrate of a common cylindrical electrophotographic photosensitive member of approximately 30 mm in inner diameter is approximately 28.5 mm, and the total length of the cylindrical substrate is approximately 360 mm when the cylindrical electrophotographic photosensitive member is to be used for the A3 paper size.
When force is applied to both end portions in the axial direction of such a long and thin insert so as to generate a pressure to press the surface (the outer peripheral surface) of the cylindrical electrophotographic photosensitive member against the molding member, such pressure tends to be unevenly applied to the vicinity of both end portions. Consequently, the depth of the uneven structure formed on the surface of the cylindrical electrophotographic photosensitive member is different, for example, in the vicinity of the central portion and in the vicinity of the end portions in the axial direction. For the purpose of suppressing such an uneven location of the pressure in the end portions and thus generating a uniform pressure distribution in the axial direction of the cylindrical electrophotographic photosensitive member, it is preferable to use an extremely firm member as the insert. Then, for the purpose of forming the insert so as to be firm, there can be used metal materials high in elastic modulus and hardness such as iron-base alloys, stainless steels and tungsten. Moreover, the shape of the insert is commonly a solid columnar shape but not a hollow columnar shape, for the purpose of more effectively ensuring the strength of the insert.